The devices of the type disclosed herein are used principally in industrial settings having exhaust duct systems with large cross sectional dimensions wherein exhaust gases must be processed by scrubbers and/or precipitators before they can be released to the air through a smokestack. An example of use for the damper of the present system would be in a power plant where combustion by-products must be released. Such combustion by-products may contain sulfur dioxide, carbon monoxide, carbon dioxide and other noxious and corrosive compounds. In addition to corrosive compounds present in the exhaust gases, temperatures within the ducts may reach highs in the range of 300° to 700° F.
It is desirable in such settings that the flow of combustion by-products through individual ducts be interrupted at various times for the purpose of performing maintenance on the scrubbers and precipitators within the exhaust system. Therefore, a typical application of the damper of the present invention would be within a duct in an exhaust system from an industrial plant to isolate a scrubber and/or a precipitator from the normal flow of combustion by-products. Because the ducts carrying the combustion by-products may be relatively large, for example, on the order of twenty-five to four hundred square feet in cross sectional area, it is possible that maintenance workers may be required to physically enter the duct to perform maintenance operations. It is therefore necessary that a seal be provided such that combustion by-products do not leak past the damper and into the area where maintenance workers may be present.
Typical prior art dampers of the type for which improvements are shown by this invention consist of a frame which is secured inline in a duct carrying combustion by-products. A blade typically slides into the cross sectional area of the duct from an area outside of the duct to close the duct, thereby interrupting the flow of the combustion by-products past the damper. In addition, to better seal the duct against leaks of the combustion by-products past the damper blade, a seal within the damper contacts the blade and is forced against the blade by an inflation pressure provided by compressed air which may be inserted into a hollow area of the seal. To open the damper it is known in the art to evacuate the air from within the seal to cause the seal to collapse away from the blade, thereby allowing the blade to be retracted to open the duct.
Such a damper is shown in U.S. Pat. No. 4,561,472 (Dryer et al.). The damper of the '472 patent is typical of those shown in the many patents of the prior art and improvements thereto are disclosed by this invention. Other similar dampers are also shown in U.S. Pat. No. 4,235,256 (Crawshay), U.S. Pat. No. 4,163,458 (Bachmann) and U.S. Pat. No. 4,022,241 (Fox).
One problem with the damper disclosed by Dryer et al. is that a failure of the seal may be precipitated by a failure of the compressed air system, which may allow the seal to deflate, thereby allowing combustion by-products to leak around the blade. A further problem with the prior art dampers of the type disclosed by Dryer et al. is that the blade, which may be subjected to differential pressure gradients and be relatively heavy, on the order of 4 plus tons, may contact the seal cartridge frame during retraction and engagement, causing galling to develop between the blade and the seal cartridge frame. This is particularly troublesome in corrosive environments where alloy materials must be utilized. Further, the mechanism for raising and lowering the blade in the prior art systems is prone to fouling by the collection of dust and dirt and through corrosion of the mechanism by continued exposure to the corrosive elements present in the combustion by-products. Lastly, the flexible seals of the prior art are typically permanently affixed to the frame of the damper, making it difficult to repair or replace the seal when necessary. These and other problems with the prior art are addressed by the current invention.